Unformatted text preview: ause they do not occur in all chordates.
b)! Because they evolved convergently in
hemichordates and cephalochordates.
c)! Because they have been further modified
within the chordates.
d)! Because they occur in other deuterostomes. dorsal tubular nerve cord neural plate begins to dip inward and the side begins to
come up become spinal cord edges closes and
neural tube detach
from the ectoderm
later it spread away spinal bifida: disorder of the neural tube development Urochordates or tunicates
•! sea squirts (ascidians) and relatives
•! sea squirts are bag-like, with enlarged
perforated pharynx for filter-feeding Why a chordate? Because urochordate larvae show all the chordate characters
dorsal hollow nerve
endostyle/thyroid Is this an ancestral
urochordate body plan? sessile Free...
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- Fall '08